Review on effects of long-lived negatively charged massive particles on Big Bang Nucleosynthesis

We review important reactions in the Big Bang Nucleosynthesis (BBN) model involving a long-lived negatively charged massive particle, X-, which is much heavier than nucleons. This model can explain the observed ⁷Li abundances of metal-poor stars, and predicts a primordial 9Be abundance that is larger than the standard BBN prediction. In the BBN epoch, nuclei recombine with the X- particle. Because of the heavy X- mass, the atomic size of bound states AX is as small as the nuclear size. The nonresonant recombination rates are then dominated by the D-wave → 2P transition for ⁷Li and 7,9Be. The 7Be destruction occurs via a recombination with the X- followed by a proton capture, and the primordial ⁷Li abundance is reduced. Also, the 9Be production occurs via the recombination of ⁷Li and X- followed by deuteron capture. The initial abundance and the lifetime of the X- particles are constrained from a BBN reaction network calculation. We derived parameter region for the ⁷Li reduction allowed in supersymmetric or Kaluza- Klein (KK) models. We find that either the selectron, smuon, KK electron or KK muon could be candidates for the X- with mX O(1) TeV, while the stau and KK tau cannot.